Add link to examples in relevant places

Some documents about driver describe a state of things that is ahead of
the reality. They already contain a warning about it, but no way to know
that the current reality is; add a pointer to a document that describes
it.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/docs/proposed/psa-driver-integration-guide.md b/docs/proposed/psa-driver-integration-guide.md
index 3d12ec6..8b3b404 100644
--- a/docs/proposed/psa-driver-integration-guide.md
+++ b/docs/proposed/psa-driver-integration-guide.md
@@ -2,6 +2,7 @@
 ==================================================
 
 **This is a specification of work in progress. The implementation is not yet merged into Mbed TLS.**
+For a description of the current state of drivers Mbed TLS, see our [PSA Cryptoprocessor driver development examples](../psa-driver-example-and-guide.html).
 
 This document describes how to build Mbed TLS with additional cryptoprocessor drivers that follow the PSA cryptoprocessor driver interface.